R. Scott Turner et al., in their U.S. patent application Ser. No. 732,946, now U.S. Pat. No. 4,121,584 entitled "Method and Apparatus for Controlling the Dispensing of Fluid" provide a significant development in controlling the rate at which an intravenous solution flows to a patient. They place a casette having a metering chamber with an inlet and an outlet in the fluid path taken by the solution as it travels to the recipient. A controller engages the casette and operates its valves. By opening the inlet and closing the outlet, the controller allows a metering chamber of known volume in the casette to fill with intravenous solution. It then closes the inlet and opens the outlet to allow that fluid to flow to the patient. It completes a cycle of operation by closing the outlet, opening the inlet, and allowing further fluid to flow into the metering chamber.
The controller includes a selection device which allows the attendant to choose the maximum rate at which the patient should receive the intravenous solution. In response to the selection thus made, the controller repeats the cycles of operation at an appropriate frequency. As a result, the separate aliquots of fluid equal in volume to the metering chamber will allow the patient to receive the desired amount of fluid during a period of time.
Turner et al.'s apparatus does not force the fluid to pass to the patient. Gravity provides the motive force causing the solution to flow. Where the fluid has an insufficient height above the point of administration, it will not pass to the patient, notwithstanding the inclusion of Turner et al.'s apparatus.
However, the equipment does serve to place an upper limit on the rate of flow of the fluid. It only allows a predetermined number of measured volumes to enter the patient's blood stream. That represents the critical limitation in the administration of intravenous solutions to an individual. If the patient receives the liquid at an excessive rate, he can suffer deleterious consequences. Even ordinary isotonic intravenous solution with only nutrients added can effectuate an unacceptable thinning of the patient's blood. Tissues depending upon the biochemicals in the blood stream can suffer when the excessive I.V. solution prohibits them from receiving these biochemicals in the required concentrations.
Excessive flow rates of intravenous solutions including medication can have drastically destructive effects upon the recipient. An inordinate concentration of the medication within the blood produces toxic effects upon the individual.
A dramatically superior casette appears in the patent application of Scott T. Garrett et al., referenced above under the title "Casette for Use with an I.V. Infusion Controller". These inventors provide a casette which sandwiches an elastomeric membrane between two sections of a rigid material, such as a plastic. The membrane forms part of the metering chamber as well as its inlet and outlet. The valving members, or rods, on the controller merely have to deform the membrane to close the appropriate opening. As a result, the controller need expend minimal energy to effectively operate the casette.
During each cycle of the operation, the controller must only move each valve member once in each of two directions. Moreover, the two valve members can couple together so that the motion of one in either direction directly accompanies the motion of the other in the opposite direction. Under these circumstances, the controller need only produce two almost insignificant motions during each cycle of operation.
With its light workload, the controller requires minimal energy to operate. Consequently, it may make use of a battery and can dispense with a direct connection to a constant source of electric power. This disencumbers the controller and allows it to travel wherever the needs of the patient may take it. Thus, it may find use at the scenes of accidents as well as accompany patients as they move about a hospital.
The longevity of a battery in the controller determines the desirability and practicality of disconnecting the controller from a constant supply of electric potential. Increasing the battery life portends the greater utilization of these devices with the concommittently increased safety for the patient.
In addition to utilizing minimal amounts of energy, the circuit should remain insensitive to broadcasted pulses of electrical energy having any appreciable strength in its environment. Additionally, the circuit must use reliable components but yet ensure that the appropriate valves in the casette remain open for sufficient periods of time.